1. Field of the Invention
This invention is directed to an improved multipiston pump for use in a vehicle brake system.
2. Description of the Prior Art
One multipiston pump is already known, for instance from U.S. Patent No. 6446435 B1 which includes a pump drive comprising a rotatably supported shaft and a single cam located on the shaft in a manner fixed against relative rotation. This cam drives an arrangement of a total of six piston pumps, which are arranged radially around the pump drive in the same plane as the pump housing. The pistons of the various piston pumps execute a reciprocating motion and are embodied as stepped pistons, to improve the intake performance. The various piston pumps are hydraulically combined into two pump units. Both pump units are in operative communication with one another on the intake side, but serve as pressure generators for two separate brake circuits of a vehicle brake system. The individual piston pumps combined into one pump unit are arranged in a star pattern and have a rotary angle spacing of 120° from each other. Moreover, the first pump unit is phase-offset from the second pump unit by a rotary angle of 30°. Thus none of the piston pumps is in phase opposition to any of the other piston pumps.
Because of this geometric arrangement of the piston pumps in the pump housing, it is attained that the intake volumetric flows of the various piston pumps sometimes overlap, in that thus the entire intake volumetric flow of the multipiston pump fluctuates with a lesser amplitude around a mean value than is true for instance in a multipiston pump with a 6×60° arrangement of the piston pumps. In other words, less pressure pulsation occurs on the intake side of the multipiston pump. This pressure pulsation can undesirably affect the brake pedal, via a master cylinder of the vehicle brake system, and be perceived by the driver.
The hydraulic combination of the various piston pumps as explained into two separate pump units is done by means of connecting conduits in the pump housing. In the known prior art, for reasons of installation space, these connecting conduits are embodied in a plurality of housing planes, which are spaced apart from the housing plane of the piston pumps. This has an adverse effect on the structural volume of the pump housing. Moreover, locating the piston pumps in the pump housing necessitates embodying the connecting conduits from a relatively large number of individual partial bores extending in different directions in space. This leads to comparatively high effort and cost for machining the pump housing, shorter service lives for the machining tools, and repeated reclamping operations during the machining process. In the subsequent work steps, some of the partial bores must be closed off again from the environment. Besides the effort and expense for assembly, this has the potential risk of leaks.
Moreover, the known arrangement makes a desired grouping of the individual Piston pumps within the pump housing more difficult and thus limits the flexibility in Structurally designing the pump housing. Aside from this, connecting bores that are Relatively long and are diverted multiple times less than the dynamics of a pressure buildup in the brake system and promote the accumulation of unwanted gas bubbles.
Against this background, the object of the present invention is to provide a multipiston pump which, with unaltered good pulsation performance, can be more easily manufactured and occupies a smaller structural volume.